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Manfred Spraul
9de5ab8a2e
sysv sem has two lock modes: One with per-semaphore locks, one lock mode with a single global lock for the whole array. When switching from the per-semaphore locks to the global lock, all per-semaphore locks must be scanned for ongoing operations. The patch adds a hysteresis for switching from the global lock to the per semaphore locks. This reduces how often the per-semaphore locks must be scanned. Compared to the initial patch, this is a simplified solution: Setting USE_GLOBAL_LOCK_HYSTERESIS to 1 restores the current behavior. In theory, a workload with exactly 10 simple sops and then one complex op now scales a bit worse, but this is pure theory: If there is concurrency, the it won't be exactly 10:1:10:1:10:1:... If there is no concurrency, then there is no need for scalability. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Manfred Spraul <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Davidlohr Bueso <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: <[email protected]> Cc: kernel test robot <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
54 lines
1.3 KiB
C
54 lines
1.3 KiB
C
#ifndef _LINUX_SEM_H
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#define _LINUX_SEM_H
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#include <linux/atomic.h>
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#include <linux/rcupdate.h>
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#include <linux/cache.h>
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#include <uapi/linux/sem.h>
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struct task_struct;
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/* One sem_array data structure for each set of semaphores in the system. */
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struct sem_array {
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struct kern_ipc_perm ____cacheline_aligned_in_smp
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sem_perm; /* permissions .. see ipc.h */
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time_t sem_ctime; /* last change time */
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struct sem *sem_base; /* ptr to first semaphore in array */
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struct list_head pending_alter; /* pending operations */
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/* that alter the array */
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struct list_head pending_const; /* pending complex operations */
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/* that do not alter semvals */
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struct list_head list_id; /* undo requests on this array */
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int sem_nsems; /* no. of semaphores in array */
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int complex_count; /* pending complex operations */
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unsigned int use_global_lock;/* >0: global lock required */
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};
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#ifdef CONFIG_SYSVIPC
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struct sysv_sem {
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struct sem_undo_list *undo_list;
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};
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extern int copy_semundo(unsigned long clone_flags, struct task_struct *tsk);
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extern void exit_sem(struct task_struct *tsk);
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#else
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struct sysv_sem {
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/* empty */
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};
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static inline int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
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{
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return 0;
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}
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static inline void exit_sem(struct task_struct *tsk)
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{
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return;
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}
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#endif
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#endif /* _LINUX_SEM_H */
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